The results of this group's previous work has suggested that joints wear out from repeated impulsive loading. The data accumulated so far is consistent with the hypothesis that repeated, physiologically reasonable, longitudinal impactions cause subchondral bone to strengthen and that this strengthened bone, being less deformable, is less effective as a shock absorber. It has been previously established that the subchondral cancellous bone acts as a major shock absorber for its overlying articular cartilage. The objective of the proposed research are: a) To establish the temporal sequence of bone and cartilage changes during the development of osteoarthritis. This will be accomplished by the controlled production of primary osteoarthritis by longitudianl impulsive loading of the hind limb of live rabbits. The sequence of cartilage and bone changes will be studied at various instants of time. b) To elucidate the relationship between the observed changes in the mechanical properties of subchondral bone and its structural changes using Materials Science techniques. c) To further validate the experimental method by studying the relationship between the joint degeneration created experimentally and human osteoarthritis by histological and chemical techniques. This work should lead to better understanding of joint degeneration and hopefully, to techniques for preventing and alleviating joint degeneration.